The histiocytic disorders are clinically heterogeneous disorders that result from an abnormal proliferation of histiocytes—either

Monocyte-macrophages (antigen-processing cells)

Dendritic cells (antigen-presenting cells)

Classifying histiocytic disorders is difficult (see Table: Histiocytic Disorders) and has changed over time as an understanding of the biology of these cells has evolved. There are other rare histiocytic disorders such as Erdheim-Chester disease, juvenile xanthogranuloma, and others.

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